HOLIVAR2006 Abstracts
Holocene climate change: evidence for solar and other forcings.
Jürg Beer
EAWAG, Ueberlandstr. 133, CH-8600 Duebendorf, Switzerland
Contact: Jürg Beer (beer@eawag.ch)
With the growing number of high-resolution high-quality climate reconstructions an increasingly clear picture emerges of a climatically variable Holocene. This raises the question of what causes these changes. While during the pre-industrial era greenhouse gases measured in air bubbles of ice cores do not show much variability and seem to play only a minor role, we are mainly left with solar and volcanic forcing and potential interior variability of the climate system. Additional, rather hypothetical, causes such as changes in the cloud cover due to changes in the cosmic ray intensity and effects of land use are still under debate.
There are two main difficulties in attributing the correct causes to the observed climate changes. Firstly, the absolute forcing changes are not known and must be estimated. Secondly, the response of the climate system is generally non-linear and depends strongly on feedback mechanisms with different time scales. Ultimately, a full understanding of climate changes requires appropriate climate models which take into account all the relevant processes and their couplings.
However, even with the limited information available at present it is possible to detect solar and volcanic forcing and to identify some of the underlying mechanisms.
Jürg Beer studied physics, mathematics, and astronomy at the University of Bern. There he joined the group of Prof. Oeschger where he became interested in environmental processes and climate change. In 1979, he became involved in the development of the accelerator mass spectrometry (AMS) which opened up a large variety of new applications. Cosmogenic nuclides could now be measured virtually everywhere in the environment. Jürg Beer took advantage of this unique opportunity and started to explore potential applications of cosmogenic radionuclides in various natural archives. In 1987, he moved to the Swiss Federal Institute of Environmental Science and Technology (EAWAG) in Dübendorf. Since then, his group concentrates mainly on the analysis of polar ice cores and works on the reconstruction of the geomagnetic field and the solar activity and its influence on climate change. From 1994 to 1995 he spent a year at the High Altitude Observatory of the National Centre of Atmospheric Research (NCAR) in Boulder.